(1) Field of the Invention
The present invention relates to an automatic conveyance system in which the conveyance of units from a buffer storage to each test cell is automated.
A product manufacturing line is generally divided into an assembly line and a test line. When one product consists of only one unit such as a printed board unit, the assembly and the testing of the product are easily coupled directly. For the assembly and for the testing, a conveyer is generally used as a material handling device.
When one product consists of a number of units, however, and when the kinds of units tested are different when each unit is tested (for example, when the constitutions of measuring devices for a digital/analog conversion circuit, a low frequency circuit, a high frequency circuit, a microwave circuit and so forth are greatly different), lines or testing devices are arranged for respective kinds of units. To synchronize with the assembly process, a buffer storage is provided. The subject of the present invention is, for example in a testing process, related to a material distribution from the entering of a unit into a process to the removal of the unit from the process.
(2) Description of the Related Art
Conventionally, a number of unit shelves each including the same kinds of units are received at a receiving port and stored in a buffer storage. Test cells are arranged in a matrix, and beside each test cell, an operator is present to perform necessary tests on the units in a unit rack which was conveyed from the buffer storage. The unit rack, including units on which the test has completed, is returned from the test cell to the buffer storage.
As a means for automating the distribution of the units from the buffer storage to respective test cells, a conveyer, an automatic guided vehicle a linear motor car, and so forth have been conventionally considered. When the conveyer or the linear motor car is used, however, once the conveyance path is arranged, it is difficult to change the layout so that the flexibility in terms of modification of the system is low and the cost is excessive. For the flexibility, however, the automatic guided vehicle is advantageous.
In the conventional conveyance using an automatic guided vehicle, however, there are problems as described later in detail.
Because of the above disadvantages, conventionally, the conveyance by an automatic guided vehicle is limited to a very simple operation with a relatively small number of stations.